1. Field of the Invention
The present invention relates to a frequency demodulating circuit, optical disk apparatus and preformatting device.
2. Description of Related Art
In the conventional art, an optical disk has been proposed in which frequency modulation of biphase modulated address information ADM is performed and grooves are recorded in a wobbling state corresponding to the post-modulated signal. This groove wobble as shown in FIG. 40 may for instance, when the digital data is xe2x80x9c1xe2x80x9d per one bit (biphase 1 bit) of the address information ADM, become 4.25 waves (period of 4.25 on the sine wave), whereas when the digital data is xe2x80x9c0xe2x80x9d per a biphase 1 bit of the address information ADM, the groove wobble becomes 3.75 waves (period of 3.75 on the sine wave). In this case, the groove wobble is a fixed amount regardless of the frequencies of the post-modulated signals.
FIG. 41 is a block diagram showing a sample layout of a frequency demodulating circuit 100 of the conventional art used to acquire address information ADM from a groove wobble reproduction signal, in other words a wobble signal SWB. This frequency demodulating circuit 100 contains a capacitor 101 for blocking the DC component, and a comparator 102 for converting the wobble signal SWB into the binary signal PWB whose DC component has been removed by setting a threshold value of zero.
Also, the frequency demodulating circuit 100 includes a voltage-controlled oscillator 103a, a phase comparator 103b, and also a low-pass filter 103c, which constitute a PLL (phase-locked loop) circuit 103. The phase comparator 103b compares the phases of the output signal of this voltage-controlled oscillator 103a and the pulse signal PWB output from the comparator 102. The low-pass filter 103c derives the low frequency component of the phase error signal output from this phase comparator 103b in order to obtain a control signal which is supplied to the voltage-controlled oscillator 103a. 
This frequency demodulating circuit 100 also contains another low-pass filter 104 for deriving the low frequency component of an output signal from the low-pass filter 103c; another capacitor 105 for removing the DC component; and another comparator 106 to acquire the address information ADM from the output signal of the low-pass filter 104, whose DC component is removed while setting a threshold value of zero.
Also, the frequency demodulating circuit 100 contains an edge detector 107 for detecting a rising edge and falling edge of the address information ADM output from the comparator 106; and a monostable multivibrator 108 capable of obtaining a pulse signal of a predetermined width while using an edge detection signal output from this edge detector 107.
The frequency demodulating circuit 100 further includes another voltage-controlled oscillator 109a, another phase comparator 109b, and another low-pass filter 109c, which constitutes another PLL circuit 109. The phase comparator 109b executes a phase comparison between the output signal of this voltage-controlled oscillator 109a and the pulse signal output from the monostable multivibrator 108. The low-pass filter 109c derives a low frequency component from a phase error signal output from this phase comparator 109b in order to produce a control signal which is supplied to the voltage-controlled oscillator 109a. 
The operation of the frequency demodulating circuit 100 shown in FIG. 41 will next be described. The wobble signal SWB is supplied via the capacitor 101 to the comparator 102 in order to be converted into a binary signal PWB. As previously described, the address information ADM which has been biphase-modulated is frequency-modulated, and this frequency-modulated signal is recorded as a groove wobble on the optical disk. As a result, as shown in FIG. 42A, the wobble signal SWB has 4.25 waves when the digital data is xe2x80x9c1xe2x80x9d, and has 3.75 waves when the digital data is xe2x80x9c0xe2x80x9d in correspondence with the 1 bit (biphase 1 bit) of the address information ADM similar to the frequency-modulated signal. Such a binary signal PWB as shown in FIG. 42B is therefore output from the comparator 102.
On the other hand, since the frequency of the wobble signal SWB corresponding to xe2x80x9c1xe2x80x9d is different from the frequency of the wobble signal SWB corresponding to xe2x80x9c0xe2x80x9d, the output signal of the low-pass filter 103c which constitutes the PLL circuit 103 is shown in FIG. 42C. As a result, the address information ADM is produced from the low-pass filter 106, as indicated in FIG. 42D. The edge of this address information ADM is then detected by the edge detector 107. The edge detection signal is supplied as a trigger signal to the PLL circuit 109 and the pulse signal output from the monostable multivibrator 108 is supplied as a reference signal to this PLL circuit 109. As a result, a clock signal xe2x80x9cACKxe2x80x9d which is synchronized with the address information is acquired from the voltage-controlled oscillator 109a to constitute the PLL circuit 109 as shown in FIG. 42E.
As previously described, the frequency demodulating circuit 100 shown in FIG. 41 has two signal systems of the PLL circuits 103 and 109 which constitute an overly complex circuit configuration.
As explained previously, the amplitude of the wobble groove recorded on the optical disk is a fixed amount regardless of the frequency of the signal after modulation so that as shown in the enlarged view in FIG. 40, a change in the slope (or deflection) occurs at the zero crosspoint of the groove wobble corresponding to the junction of the xe2x80x9c1xe2x80x9d and the xe2x80x9c0xe2x80x9d of the address information ADM. Consequently, large jitter is prone to occur on the time axis of the wobble signal SWB that matches the junction point of the xe2x80x9c1xe2x80x9d and the xe2x80x9c0xe2x80x9d of the address information ADM. This jitter prevents the demodulation circuit from acquiring error-free address information ADM.
The assignee of this invention and others are currently in the midst of developing the next generation of optical magnetic disks (ASMO) and are proposing an magneto-optical disk in which clock marks hold address information by means of the groove wobbles and preformatting is performed. In this previously undisclosed magneto-optical disk apparatus, a data clock signal is acquired in order to record and reproduce data by utilizing the reproduction signal of this clock mark.
A reproduction signal SCM of the clock marks is shown in FIG. 43A. This reproduction signal SCM functions as shown in FIG. 43B to form a PCM signal showing the timing of the zero (0) crosspoint. A data clock signal is acquired by means of the PLL circuit while referring to this pulse PCM signal.
The above mentioned clock mark CM is formed as shown in FIGS. 44A and 44B while using a pair of cutting beams to cut-forme the surface of the base disk. Writing is performed radially across the surface of the disk base with a lands 12L and a grooves 12b being alternately formed. The groove 12G is cut to a specified depth Da as shown in the cross sectional view in FIG. 44B by using the cutting beams. Excluding the beams Ba, Bb, FIG. 44 shows a lateral reduction of one-tenth when the vertical direction is set as 1, just the same as in FIG. 45 related later.
The flat surface is one side of the cutting edge 11a in the groove 12G and the other cutting edge 11b is wobbled. The address information (shown by sine wave) ADM and the clockmark CM (one cycle of sine wave) are consecutively formed in this address information ADM (shown by sine wave).
One pair of cutting beams Ba, Bb is used as shown in FIG. 44A as the cutting beams for performing wobble cutting. The cutting beams Ba, Bb scan the surface of the base disk in a partially overlapping state as shown in the figure. In this example, a groove wobble is formed by means of the cutting beam Ba.
When reproducing the clock mark CM formed in the groove 12G in the groove wobble by means of the PPB beam shown in FIG. 45, both the reproduction signal SCM of the clock mark CM acquired during scanning of the land 12L and the reproduction signal SCM of the clock mark CM acquired during scanning of the groove 12G form signals of identical polarity as shown in FIG. 43A.
Accordingly, whether the beam PPB is scanning above the land 12L or scanning above the groove 12G cannot currently be determined by means of this reproduction signal SCM. However, if it can be determined from the polarity of the reproduction signal SCM, whether the beam PPB is currently scanning above the land 12L or scanning above the groove 12G, and servo control of the optical pickup system can then be accurately performed.
Further, as related above, the amplitude Wa (FIG. 44A) of the clock mark formed in the groove 12G by means of the wobble groove, is extremely small. The clock mark CM for the reproduction signal SCM shown in FIG. 43A has a poor signal to noise ratio. Accordingly, the clock signal acquired by using this reproduction signal SCM has a large jitter and for instance cannot be used as a clock signal for data reproduction. Further, control of the first cutting beam Ba is difficult since the clock signal must be formed accompanied by drastic level fluctuations of the zero cross point, the smaller the amplitude Wa.
It is therefore an object of this invention to provide an optical disk apparatus in which one signal system of these PLL circuits is reduced to a simple configuration for performing demodulation.
It is therefore another object of this invention to provide an optical disk apparatus in which jitter is reduced at the time axis of the wobble signal SWB that matches the junction point of the xe2x80x9c1xe2x80x9d and the xe2x80x9c0xe2x80x9d of the address information ADM and thus allow satisfactory acquisition of address information.
It is still another object of this invention to provide a preformatting device that can easily preformat marks having highly precise position (phase) information.
It is a further object of this invention to provide an optical disk apparatus that easily identifies whether the beam is above the groove or above the land by utilizing a polarized reproduction signal of a mark having phase information to determine whether the beam scanning the optical disk is above the land or above the groove.
In the optical disk apparatus of one aspect of this invention for driving an optical disk on which a groove wobble corresponding to a signal acquired from frequency modulated, biphase modulated address information, and a mark for expressing phase information placed inside said wobble are preformatted; and along with making the biphase bit count xe2x80x9caxe2x80x9d (xe2x80x9caxe2x80x9d is a natural number) between two of adjacent said marks, the channel bit count is made xe2x80x9cnxe2x80x9d (xe2x80x9cnxe2x80x9d is a natural number) between two of said adjacent marks wherein, said optical disk has first clock signal reproduction means to generate a first clock signal utilizing an xe2x80x9cnxe2x80x9d frequency multiple of the reproduction signal of said clock mark and, wobble signal reproduction means to reproduce from said optical disk a wobble signal corresponding to said groove wobble and, frequency demodulation means to acquire said address information by frequency demodulation of said wobble signal and, said frequency demodulation means has; a second clock signal generator to generate a second clock signal by dividing a data clock signal supplied from said first clock signal reproduction means by 1/M(M=n/(axc2x7s)) in which a clock xe2x80x9csxe2x80x9d (xe2x80x9csxe2x80x9d is a natural number) is an oversampling value of said biphase bit and a waveform shaping unit to shape the waveform of said wobble signal and a detector to acquire said address information by processing with said second clock signal for said binary signal.
In this invention therefore, a biphase bit oversampling clock signal is generated by frequency division from a data clock signal which is an integer ratio of data clock signal and frequency of the biphase bit oversampling clock signal. Utilizing this clock signal allows acquisition of address information by frequency demodulation of the wobble signal obtained with the wobble signal reproduction means.
A optical disk apparatus of another aspect of this invention for driving an optical disk formed with alternate grooves and lands radially across the disk surface containing recording tracks; and marks preformatted with phase information wherein; marks having said phase information are formed on one end of said land or said groove and have a first concavity or protrusion at parallel falling sides in said radial direction and, a said land or said groove formed on the other side, parallel in the radial direction and constituting a second concavity or protrusion in the track rising direction also matching the falling direction, and whether the laser beam scanning said optical disk is above said land or above said groove can be detected from the polarity of the reproduction signal on the mark.
In a further aspect of this invention, in the lands and grooves, the concavities and protrusions comprising the marks containing the phase information, protrude in opposite directions. Consequently, the polarity of the mark reproduction signal will have a respectively different polarity according to whether the beam is scanning a land or a groove. This means that whether the beam is over a groove or a land can easily be determined by means of the polarity of the mark reproduction signal.
A preformatting device in yet another aspect of this invention is provided for cut-forming the surface of the base disk to form grooves and marks containing phase information on said base disk wherein said preformatting device comprises: a light source for generating a first and a second cutting beam, optical means for joining said first and second cutting beams to mutually overlap so that said first and second cutting beams overlap to irradiate a portion of the surface of the base disk, cutting beam control means for controlling on and off switching of said first and second cutting beams and, control means for controlling operation of said cutting beam control means. The control means is regulated such that said first cutting beam is turned off only for a fixed period immediately before the timing of said mark to be formed, and said second cutting beam is turned off only for a fixed period immediately after the timing of said mark to be formed.
In a yet further aspect of this invention, a first and a second cutting beam overlap and the junction of their light beams irradiates the surface of the base disk and cut-forms a groove in that surface. The first cutting beam is turned off for a fixed period immediately before the timing of said mark to be formed, and at one side of the groove, a protrusion is formed in parallel in the falling section towards the track where the mark is to be formed in the radial direction of the disk. The second cutting beam turns off for a fixed interval immediately after the timing of the mark to be formed. Accordingly, a protrusion is formed on the other side of the groove in parallel in the rising section towards the track where the mark is to be formed in the radial direction of the disk. The pairs of protrusions formed in these grooves are marks having phase information.
In the optical disk preformatted with the marks having the phase information as described above, when a mark is scanned by a beam, a signal having a one cycle sine wave is acquired. As related above, since the mark is formed by controlling the on and off switching of the cutting beam, the mark reproduction signal undergoes a sudden level change at the zero crosspoint. Consequently, the zero crosspoint can accurately be detected with no effect from jitter, even if the amount of protrusion from the pair of protrusions comprising the marks is small.
In a still further aspect of this invention, a frequency demodulator circuit has a waveform shaping section for forming a frequency modulated signal expressing the digital data to acquire a binary signal, clock signal generating unit for generating clock signals having a frequency corresponding to xe2x80x9c1xe2x80x9d of said address information, and also having a frequency higher than said frequency signal by a common multiple, which corresponds to xe2x80x9c0xe2x80x9d of said digital data; and a detector for acquiring said digital data based on clock signals corresponding to said binary information.
The optical disk apparatus of this invention further drives an optical disk on which a groove wobble corresponding to a signal acquired from frequency modulated address information, and a post-modulated signal are recorded; wobble signal reproduction means for reproducing from said optical disk a wobble signal corresponding to said groove wobble and, frequency demodulation means for acquiring said address information by frequency demodulation of said wobble signal and said frequency demodulation means has :a waveform shaping unit for acquiring a binary signal from a wave shaped from the wobble signal, a wobble signal frequency corresponding to said address information of xe2x80x9c1xe2x80x9d, clock signal generator means for acquiring a clock signal having a frequency multiple of said wobble signal corresponding to said address information of xe2x80x9c0xe2x80x9d, a detector for acquiring said address information by processing said binary signal with said clock signal.
In this aspect of the invention, the digital data, for instance the frequency modulated signal containing address information is shaped by a waveform shaping unit and converted into a binary signal. Then a clock signal generator, for instance a PLL circuit is used to obtain a clock signal which is a common multiple (for instance the lowest common multiple frequency) higher than the frequency modulated signal corresponding respectively to the digital data xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d.
Based on this clock signal, the binary signal corresponding to xe2x80x9c1xe2x80x9d has a pattern of xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d comprised of the first clock portion; and the binary signal corresponding to xe2x80x9c0xe2x80x9d has a pattern of xe2x80x9c1xe2x80x9d and xe2x80x9c0xe2x80x9d comprised of the second clock portion. In the detector, a binary signal pattern using this clock signal is detected and demodulation of the digital data then performed.
In an optical disk apparatus of a further aspect of this invention in which the address information is frequency modulated and the post-modulation signal is recorded on an optical disk as a groove wobble. This groove wobble amplitude is made to change according to the frequency of the signal after modulation. This change in groove wobble amplitude prevents a deflection near the groove wobble zero crosspoint corresponding to the junction point of the waveform expressing xe2x80x9c0xe2x80x9d and the waveform expressing xe2x80x9c1xe2x80x9d of the address information.
In this invention, the groove wobble amplitude is made to change according to the frequency of the signal after modulation, and a fixed amount of deflection is applied to the groove wobble zero crosspoint corresponding to the junction point of the waveform expressing xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d of the address information. This process reduces jitter along the time axis of the wobble signal SWB corresponding to the junction of the xe2x80x9c0xe2x80x9d and xe2x80x9c1xe2x80x9d of the address information.